The present application relates to technology for performing pattern processing on a transparent conductive film that is used for a transparent electrode on a multilayer thin film of a FPD (Flat Panel Display) and the like. Particularly the present application relates to a laser processing apparatus, a laser processing head and a laser processing method for removing and extracting debris that is particles and products generated during laser processing based on ablation, thermofusion, or composite action thereof in which a surface of a processing object is irradiated with laser light.
A transparent conductive film is used as a transparent electrode of an array substrate (multilayer film substrate) for a flat display panel, of a solar cell and the like. Also a transparent conductive film is widely adopted as a transparent electrode in the field of electronic paper whose development has been promoted as a future display device, and the use thereof has been expanded. Further, since competition for higher definition and lower costs of a display has become more intensive recently, a transparent conductive film of higher quality and higher productivity may also be required in manufacturing.
Such transparent conductive film is typically patterned into a desired shape by a photolithography method. For example, a transparent conductive film made of an ITO (Indium Tin Oxides) film, a ZnO (Zinc Oxides) film or the like is vacuum-coated on a glass, plastic, or silicon wafer substrate or the like, then a resist layer is formed thereon to obtain a multilayer thin film. The resist layer is exposed by irradiation of light through a photomask having a predetermined pattern. The photomask pattern is transcribed onto the resist layer by performing development and post bake, then a portion of the transparent conductive film not covered with the resist is removed by an etching method, and the remaining resist layer is removed at the end so that the desired pattern of the transparent conductive film is obtained.
However, the photolithography process described above needs a large scale apparatus such as a coater/developer, which discourages manufacturing costs from being reduced. In addition, since a large amount of chemical solution such as developing solution is used, there is also caused a problem in view of environmental preservation. Furthermore, a low-temperature polysilicon liquid crystal display of reflective and transmissible type, for example, includes an ITO film used as a transmissible portion of a pixel electrode and an Al film or the like used as a reflective film on a substrate provided with a TFT (Thin Film Transistor). In this case, the photolithography process is needed twice since the resist and development solution are different even if the same pattern form is used in each patterning. Accordingly, in order to simplify a manufacturing process by omitting additional photolithography processing, Japanese Published Patent Application No. 2004-153171, for example, discloses technology for directly processing a transparent conductive film by using laser light.
In the above-described direct processing of a transparent conductive film by using a laser, a short wavelength laser such as an excimer laser, for example, is used. Typically, an excimer laser (excited dimmer laser) has high photon energy capable of cutting a chemical bond, and in photochemical decomposition and photothermal decomposition process called ablation using a short pulse laser of short wavelength, a processing object can be removed and minutely processed while suppressing thermal effect. Attention is focused on such laser processing technology based on the ablation. With irradiation of excimer laser light whose energy density is adjusted, various materials such as plastics (polymeric materials), metals and ceramics can be ablated.
In the ablation processing using a laser, ablation products generated from a surface of a processed object irradiated by the laser light may re-deposit around a processed region. Those ablation products are typically called debris. When re-deposition of the debris occurs around the processed region, there is a possibility that desired processing quality and processing accuracy may not be obtained. Hence, a method of reducing debris has been studied.
For example, a method (hereinafter, referred to as method 1) is proposed, in which a fluid feed apparatus for directing a fluid such as air onto a surface in the vicinity of a processed region is provided and a suction duct for sucking the fluid is installed on the opposite side to a fluid feeding nozzle. In this method 1, debris is blown away from the processed region and simultaneously is sucked and removed (see, Japanese Published Patent Application No. 10-99978).
Further, it is known that blowing an assist gas around a laser light irradiated region together with irradiation of laser light onto the processing object is efficient for reducing an amount of debris generated. A method (hereinafter, referred to as method 2) is proposed, in which a laser processing head includes an inner side nozzle and an outer side nozzle arranged surrounding an outer circumferential surface thereof are disposed. In this method 2, an assist gas is directed toward a processed region from the inner side nozzle, and debris is extracted by sucking the assist gas using the outer side nozzle (see, Japanese Published Patent Application No. 09-192870). Further, a method of decomposing debris or preventing re-deposition thereof by using a predetermined atmospheric gas is known as a method of controlling generation itself of debris. Furthermore, it is known that an amount of debris deposited on the processed object can be greatly reduced by performing the laser processing under low pressure conditions of about 10[Pa] (10−2 Torr).
Further, as shown in FIG. 1, a method (hereinafter, referred to as method 3) is proposed, in which an opening portion 120 is provided right above a processing object 107 having a transparent conductive film 108b laminated on a substrate 108a, for example. In this method 3, a discharge device is provided to reduce the pressure of a region surrounded by a mask or variable aperture 104 and the opening portion 120 as a closed space portion, and so debris generated by radiation of laser light 102 on the processing object 107 is discharged and also debris 121 deposits on the opening portion 120 without depositing on the processing object 107 (see, Japanese Published Patent Application No. 2004-230458).
However, debris is scattered even when suction and discharge thereof is attempted by blowing off the debris on the surface in the vicinity of the processed region as described in the method 1, and therefore it has been difficult to completely remove and extract the debris even if suction power is raised.
In addition, debris is scattered and deposits again around the processed region even when an assist gas is blown onto the processed region from the inner side nozzle as described in the method 2, and therefore it has been difficult to sufficiently remove the debris even if suction power of the outer side nozzle is increased.
Moreover, debris may not necessarily deposit at the opening portion even if pressure is reduced inside the closed space portion provided with the opening portion as described in the method 3, and therefore there has been such a problem that the debris in the center portion of the processed region re-deposits on the surface of the processing object.
In view of the problems heretofore described, there is a need for efficiently removing and extracting debris generated from laser processing, thereby reducing debris deposited on a processing object.